DE102015204093B4 - Method for suppressing ammonia slip during operation of an SCR catalytic converter of a hybrid electric drive - Google Patents

Abstract

Method for suppressing ammonia slip during operation of an SCR catalytic converter (8) of a hybrid electric drive (1), in particular a motor vehicle, the temperature of an exhaust gas from the hybrid electric drive (1) flowing through the SCR catalytic converter (8) depending on a predetermined limit temperature of the SCR -Catalyst (8), beyond which an uncontrolled release of ammonia stored in the SCR catalyst (8) occurs, is regulated in such a way that a temperature of the SCR catalyst (8) does not exceed the predetermined limit temperature, a space velocity of the SCR -Catalyst (8) depending on the specified limit temperature of the SCR catalyst (8) is regulated in such a way that the temperature of the SCR catalyst (8) does not exceed the specified limit temperature and the space velocity of the SCR catalyst (8) is controlled by Parameters of an exhaust gas recirculation of the hybrid electric drive (1) and / or parameters of a cylinder The filling of cylinders of the internal combustion engine (3) is regulated.

Description

The invention relates to a method for suppressing ammonia slip during operation of an SCR catalytic converter of a hybrid electric drive, in particular of a motor vehicle.

The invention also relates to a hybrid electric drive, in particular for a motor vehicle, having at least one electric motor and at least one internal combustion engine, with each of which a drive power can be provided, and at least one SCR catalytic converter connected downstream of the internal combustion engine.

Exhaust gases from an internal combustion engine, for example an Otto engine or a diesel engine, can be treated with an exhaust gas aftertreatment system connected downstream of the internal combustion engine in order to reduce pollutant emissions. The effectiveness of an exhaust aftertreatment system is influenced, among other things, by the temperature level in the exhaust aftertreatment system.

An exhaust gas aftertreatment system can have a catalytic converter set up for selective catalytic reduction (“SCR catalytic converter”), with which nitrogen oxides (NO _x ) can be reduced to nitrogen and water. However, an SCR catalytic converter can only reduce nitrogen oxides when it has reached a characteristic operating temperature, the so-called light-off temperature.

DE 103 33 210 A1 discloses a hybrid vehicle with a hybrid electric drive which has at least one electric motor and at least one internal combustion engine, with each of which drive power can be provided, and at least one exhaust gas aftertreatment system connected downstream of the internal combustion engine. The exhaust gas aftertreatment system comprises a 3-way catalytic converter and an NO _x storage catalytic converter connected downstream of the 3-way catalytic converter. According to DE 103 33 210 A1 is to be influenced by an optimized torque output of the internal combustion engine and the electric motor, a conversion activity of the exhaust gas aftertreatment system to achieve a predetermined conversion threshold value. For this purpose, the value of the conversion activity is determined for at least one component of the exhaust gas aftertreatment system and, if this value is below the specified conversion threshold, the torque output of the electric motor is increased and the torque output of the internal combustion engine is reduced compared to an operation of the hybrid electric drive without providing torque by the electric motor. As a result, the conversion activity of the exhaust gas aftertreatment system can be improved, as a result of which pollutant emissions from the hybrid electric drive can be reduced.

DE 10 2010 037 924 A1 relates to a method for controlling an exhaust gas aftertreatment system of a hybrid electric drive, with which an optimal operation of the exhaust gas aftertreatment system with regard to the exhaust gas cleaning and conversion performance is to be made possible. For this purpose, the operating mode of the hybrid electric drive is selected as a function of a specifiable temperature or a specifiable space velocity of the exhaust gas aftertreatment system.

WO 2011/114 028 A1 discloses a method for treating nitrogen oxides that are contained in an exhaust gas of a hybrid electric drive. For this purpose, a likely associated temperature of an SCR catalytic converter downstream of an internal combustion engine of the hybrid electric drive is determined for a drive torque request, which would occur if the requested drive torque were applied by the internal combustion engine alone. This temperature is compared with a reference temperature at which an optimal reduction of the nitrogen oxides would take place in the SCR catalytic converter. If the predetermined temperature is above the reference temperature, at least part of the requested drive torque is applied by an electric motor of the hybrid electric drive.

JP 2010 - 90 723 A relates to a method for operating a hybrid electric drive, according to which a drive torque to be applied is at least partially applied by an electric motor of the hybrid electric drive when the amount of ammonia contained in an SCR catalytic converter connected downstream of the internal combustion engine of the hybrid electric drive falls below a predetermined limit value.

DE 10 2009 054 046 A1 describes a method for operating an internal combustion engine. In the context of the method, the internal combustion engine is controlled, in particular with regard to an air-fuel ratio, in such a way that preferred concentrations of nitrogen oxide, carbon monoxide and hydrogen occur in the exhaust gas.

DE 10 2012 218 119 A1 describes a method for operating a drive train with an internal combustion engine and an electric motor. The drive train is operated in such a way that a temperature of at least one exhaust gas aftertreatment component is increased when this temperature is below a temperature threshold value.

The object of the invention is to reduce the operational nitrogen oxide emissions of a hybrid electric drive and to reduce ammonia slip in an SCR catalytic converter as far as possible.

This object is achieved by a method for suppressing ammonia slip according to claim 1 or by a hybrid drive according to claim 5. Advantageous refinements are given in particular in the dependent claims, each of which taken alone or in various combinations with one another can represent an aspect of the invention.

According to the method according to the invention for suppressing ammonia slip during operation of an SCR catalytic converter of a hybrid electric drive, in particular of a motor vehicle, a temperature of an exhaust gas from the hybrid electric drive flowing through the SCR catalytic converter is determined as a function of a predetermined limit temperature of the SCR catalytic converter, beyond which an uncontrolled release of ammonia stored in the SCR catalytic converter takes place, regulated in such a way that a temperature of the SCR catalytic converter does not exceed the predetermined limit temperature.

According to the invention, the ammonia slip of the SCR catalytic converter is taken into account when the hybrid electric drive is operated in order to reduce the ammonia slip as far as possible or completely. For this purpose, the temperature of the SCR catalytic converter is recorded and compared with the predetermined limit temperature, beyond which an uncontrolled release of ammonia stored in the SCR catalytic converter takes place. By regulating the exhaust gas temperature according to the invention, the application of heat to the SCR catalytic converter is regulated in order to prevent the predetermined limit temperature from being exceeded.

The SCR catalytic converter stores ammonia, which can be sprayed upstream of the SCR catalytic converter into an exhaust line leading to the SCR catalytic converter. This type of exhaust aftertreatment is known as active selective catalytic reduction. The hybrid electric drive can have a nitrogen oxide storage catalytic converter connected upstream of the SCR catalytic converter, with which, for example, nitrogen oxides can be removed from the exhaust gas before the SCR catalytic converter has reached its characteristic light-off temperature. The nitrogen oxide storage catalytic converter can be regenerated by a rich operation of the internal combustion engine of the hybrid electric drive, whereby it is stimulated to release the nitrogen oxides temporarily stored in it. Here, ammonia can be formed in the nitrogen oxide storage catalytic converter, which gets into the SCR catalytic converter and is stored there. This type of exhaust aftertreatment is known as passive selective catalytic reduction.

Ideally, all nitrogen oxides contained in the exhaust gas are converted into nitrogen using the ammonia present in the SCR catalytic converter. The operation of the SCR catalytic converter, in particular with regard to the reduction of nitrogen oxides, depends on the operating temperature of the SCR catalytic converter, its space velocity and the amount of ammonia it contains. At high operating temperatures, the ammonia oxidizes and can form nitrogen oxides. This is associated with a deteriorated reduction performance of the SCR catalytic converter. At high operating temperatures, the ammonia stored in the SCR catalytic converter is also at least partially desorbed, which is associated with an undesired ammonia slip and also with a deteriorated reduction performance of the SCR catalytic converter.

These disadvantages at high operating temperatures of the SCR catalytic converter can be prevented by the method according to the invention, since the temperature of the SCR catalytic converter is limited to the predetermined limit temperature so that no ammonia slip and preferably also no oxidation of the ammonia present in the SCR catalytic converter occurs. This makes use of the fact that in a hybrid electric drive, a drive torque applied by the hybrid electric drive can be divided between the internal combustion engine and the electric motor, whereby the operation of the internal combustion engine and thus the temperature of its exhaust gas can be influenced.

By means of the method according to the invention, the SCR catalytic converter can be operated in a temperature range that is optimal with regard to the ammonia slip and its reduction performance. The hybrid electric drive can also be operated during a cold start phase of the internal combustion engine in such a way that the SCR catalytic converter reaches its light-off temperature as quickly as possible. This can be done, for example, in that the electric motor is used in generator mode during the cold start phase and the internal combustion engine is used to drive the electric motor.

The inventive regulation of the exhaust gas temperature could also take place as a function of a temperature that is a certain value less than the predetermined limit temperature, beyond which an uncontrolled release of ammonia stored in the SCR catalytic converter takes place. Due to this fixed relationship between the temperature and the predetermined limit temperature, the exhaust gas temperature would nevertheless be regulated as a function of the predetermined limit temperature in accordance with the invention.

According to an advantageous embodiment, the temperature of the exhaust gas is regulated by at least partially applying a drive torque generated by the hybrid electric drive by at least one electric motor of the hybrid electric drive when the predetermined limit temperature is reached. As a result, the load applied to the internal combustion engine is reduced or the drive torque applied by the internal combustion engine is reduced. This is accompanied by a reduction in the temperature of the exhaust gases from the internal combustion engine. In particular, during acceleration processes or at high driving speeds, the internal combustion engine can be appropriately supported by the electric motor.

When the predetermined limit temperature is reached, a maximum drive torque that can be generated by an internal combustion engine of the hybrid electric drive is advantageously limited to a predetermined maximum drive torque. This prevents the internal combustion engine from being operated in a power range with which high exhaust gas temperatures are associated.

In the context of the present invention, a space velocity of the SCR catalytic converter is regulated as a function of the predefined limit temperature of the SCR catalytic converter in such a way that the temperature of the SCR catalytic converter does not exceed the predefined limit temperature. The space velocity of the SCR catalytic converter also has an influence on the storage behavior of the SCR catalytic converter with regard to ammonia storage. At high space velocities, there is a greater heat transfer to the SCR catalytic converter, as a result of which the temperature of the SCR catalytic converter is increased, which is associated with the disadvantages mentioned above. In particular, at high space velocities, the ammonia stored in the SCR catalytic converter can be desorbed, which is associated with undesired ammonia slip. This is prevented by this embodiment of the method according to the invention in that the space velocity is kept low or the internal combustion engine is operated in such a way that low space velocities occur.

The space velocity of the SCR catalytic converter is regulated by regulating parameters of exhaust gas recirculation of the hybrid electric drive and / or of parameters of cylinder filling of cylinders of the internal combustion engine. This can take place in particular if the hybrid electric drive is designed as a mild hybrid. The parameters of the exhaust gas recirculation can be influenced, for example, in such a way that a flap present in the exhaust gas recirculation is opened or closed correspondingly wide. The cylinder charge can be regulated, for example, by varying the opening and / or closing times of inlet and / or outlet valves of the internal combustion engine.

A further advantageous embodiment provides that a space velocity of the SCR catalytic converter is regulated by regulating an engine speed of the internal combustion engine. This refinement is suitable for a hybrid electric drive that is designed as a full hybrid. With such a hybrid electric drive, both the drive torque and the engine speed can be regulated. The latter has an influence on the space velocity, the engine speed of the internal combustion engine being reduced in order to reduce the space velocity.

• - wenigstens einen Elektromotor und wenigstens einen Verbrennungsmotor, mit denen jeweils eine Antriebsleistung bereitstellbar ist,
• - wenigstens einen dem Verbrennungsmotor nachgeschalteten SCR-Katalysator,
• - wenigstens eine Sensoreinrichtung zum Erfassen einer Temperatur des SCR-Katalysators, mit welcher der jeweilig erfassten Temperatur des SCR-Katalysators entsprechende, dem SCR-Katalysator zugeordnete Temperatursignale erzeugbar sind, und
• - wenigstens eine Steuer- und/oder Regelelektronik, die signaltechnisch mit dem Elektromotor, dem Verbrennungsmotor und der Sensoreinrichtung verbunden und zum Ansteuern des Elektromotors und des Verbrennungsmotors eingerichtet ist,
• - wobei die Steuer- und/oder Regelelektronik eingerichtet ist, aus den dem SCR-Katalysator zugeordneten Temperatursignalen zu ermitteln, ob die Temperatur des SCR-Katalysators eine vorgegebene Grenztemperatur des SCR-Katalysators, ab deren Überschreitung eine unkontrollierte Freisetzung von in dem SCR-Katalysator gespeichertem Ammoniak erfolgt, erreicht hat und, nachdem die Temperatur des SCR-Katalysators die vorgegebene Grenztemperatur erreicht hat,
• - zumindest zeitweilig den Elektromotor und den Verbrennungsmotor derart anzusteuern, dass ein von dem Hybridelektroantrieb erzeugtes Antriebsdrehmoment zumindest teilweise von dem Elektromotor aufbringbar ist.

The hybrid electric drive according to the invention, in particular for a motor vehicle, includes

• - at least one electric motor and at least one internal combustion engine, with each of which a drive power can be provided,
• - At least one SCR catalytic converter downstream of the internal combustion engine,
• - At least one sensor device for detecting a temperature of the SCR catalytic converter, with which temperature signals corresponding to the respectively detected temperature of the SCR catalytic converter and assigned to the SCR catalytic converter can be generated, and
• - At least one control and / or regulating electronics, which is signal-connected to the electric motor, the internal combustion engine and the sensor device and is set up to control the electric motor and the internal combustion engine,
• - The control and / or regulating electronics being set up to determine from the temperature signals assigned to the SCR catalytic converter whether the temperature of the SCR catalytic converter is a predetermined limit temperature of the SCR catalytic converter and, if this limit temperature is exceeded, an uncontrolled release of in the SCR catalytic converter stored ammonia takes place, has reached and, after the temperature of the SCR catalytic converter has reached the specified limit temperature,
• - at least temporarily to control the electric motor and the internal combustion engine in such a way that a drive torque generated by the hybrid electric drive can at least partially be applied by the electric motor.

The advantages mentioned above with reference to the method are correspondingly associated with the hybrid electric drive. In particular, the hybrid electric drive can be used to carry out the method be set up. The hybrid electric drive can be designed as a serial or parallel hybrid electric drive. The hybrid electric drive can be designed, for example, as a full hybrid or as a mild hybrid.

The hybrid electric drive can have a single electric motor with which at least two wheels of the motor vehicle can be driven. Alternatively, the hybrid electric drive can each have its own electric motor for at least two wheels.

The internal combustion engine is preferably a diesel engine. The hybrid electric drive can additionally have at least one diesel oxidation catalytic converter connected upstream of the SCR catalytic converter and at least one soot particle filter which is arranged separately from the SCR catalytic converter or combined with it to form an exhaust gas aftertreatment unit.

The SCR catalytic converter can be arranged at any point in the exhaust system. It can be arranged close to the internal combustion engine or under a vehicle floor. The closer the SCR catalytic converter is arranged to the internal combustion engine and the fewer further catalytic converter components are arranged between the SCR catalytic converter and the internal combustion engine, the more the temperature of the SCR catalytic converter is influenced by the operating state of the internal combustion engine.

The sensor device for detecting the temperature of the SCR catalytic converter can have at least one temperature sensor arranged on the SCR catalytic converter. The sensor device can be wired or wirelessly connected to the control and / or regulating electronics using signals.

According to an advantageous embodiment, the control and / or regulating electronics are set up to limit a maximum drive torque that can be generated by the internal combustion engine to a specified maximum drive torque after the temperature of the SCR catalytic converter has reached the specified limit temperature. The advantages mentioned above with reference to the corresponding embodiment of the method are correspondingly associated with this embodiment.

According to a further advantageous embodiment, the control and / or regulating electronics are set up to regulate a space velocity of the SCR catalytic converter by regulating parameters of an exhaust gas recirculation of the hybrid electric drive and / or of parameters of a cylinder filling of cylinders of the internal combustion engine, after the temperature of the SCR Catalyst has reached the specified limit temperature. The advantages mentioned above with reference to the corresponding embodiment of the method are correspondingly associated with this embodiment.

A further advantageous embodiment provides that the control and / or regulating electronics are set up to regulate a space velocity of the SCR catalytic converter by regulating an engine speed of the internal combustion engine after the temperature of the SCR catalytic converter has reached the predetermined limit temperature. The advantages mentioned above with reference to the corresponding embodiment of the method are correspondingly associated with this embodiment.

• 1 eine schematische Darstellung eines Ausführungsbeispiels für einen erfindungsgemäßen Hybridelektroantrieb; und
• 2 eine schematische Darstellung eines weiteren Ausführungsbeispiels für einen erfindungsgemäßen Hybridelektroantrieb.

In the following, the invention is explained by way of example with reference to the attached figures on the basis of preferred embodiments, the features shown below being able to represent an aspect of the invention both individually and in various combinations with one another. Show it:

• 1 a schematic representation of an embodiment for a hybrid electric drive according to the invention; and
• 2 a schematic representation of a further embodiment of a hybrid electric drive according to the invention.

Functionally identical components are provided with the same reference symbols in the figures.

1 shows a schematic representation of an exemplary embodiment for a hybrid electric drive according to the invention 1 . The hybrid electric drive 1 includes an electric motor 2 and an internal combustion engine 3 in the form of a diesel engine, with each of which drive power can be provided.

The hybrid electric drive also includes 1 one to the internal combustion engine 3 downstream exhaust aftertreatment system 4th that one the internal combustion engine 3 regarding one by the arrow 5 indicated flow direction of the exhaust gas downstream diesel oxidation catalyst 6th , one of the diesel oxidation catalyst 6th downstream soot particle filter 7th and one of the particulate filter 7th downstream SCR catalytic converter 8th having.

The hybrid electric drive 1 also includes a sensor device 9 for detecting a temperature of the SCR catalytic converter 8th with which of the respectively recorded temperature of the SCR catalytic converter 8th corresponding to the SCR catalytic converter 8th assigned temperature signals can be generated.

The hybrid electric drive also includes 1 control and / or regulation electronics 10 , which are connected to the electric motor via signal lines S for signaling purposes 2 , the internal combustion engine 3 or a motor electronics (not shown) of the internal combustion engine 3 and the sensor device 9 connected and to control the electric motor 2 and the internal combustion engine 3 is set up. In addition, the control and / or regulation electronics 10 set up from the SCR catalytic converter 8th associated temperature signals to determine whether the temperature of the SCR catalytic converter 8th a predetermined limit temperature of the SCR catalytic converter 8th , beyond which an uncontrolled release of in the SCR catalytic converter 8th stored ammonia takes place, has reached and after the temperature of the SCR catalytic converter 8th has reached the predetermined limit temperature, at least temporarily the electric motor 2 and the internal combustion engine 3 to be controlled in such a way that one of the hybrid electric drive 1 generated drive torque at least partially from the electric motor 2 is applicable.

The control and / or regulation electronics 10 is also set up a maximum of the internal combustion engine 3 to limit the generated drive torque to a predetermined maximum drive torque after the temperature of the SCR catalytic converter 8th has reached the specified limit temperature.

In addition, the control and / or regulating electronics 10 be set up a space velocity of the SCR catalyst 8th by regulating parameters of an exhaust gas recirculation (not shown) of the hybrid electric drive 1 and / or of parameters of a cylinder charge of cylinders (not shown) of the internal combustion engine 3 to regulate after the temperature of the SCR catalyst 8th has reached the specified limit temperature.

Furthermore, the control and / or regulating electronics 10 be set up a space velocity of the SCR catalyst 8th by regulating an engine speed of the internal combustion engine 3 to regulate after the temperature of the SCR catalyst 8th has reached the specified limit temperature.

2 shows a schematic representation of a further exemplary embodiment for a hybrid electric drive according to the invention 1 . This hybrid electric drive 1 only differs from the in 1 The embodiment shown, that the SCR catalytic converter with the soot particle filter to an exhaust gas aftertreatment unit 11 is summarized, instead of the SCR catalytic converter, as in 1 shown, is arranged separately from the soot particle filter. The rest of the structure of the hybrid electric drive 1 corresponds to in 1 Embodiment shown, which is why to avoid repetition on the above description of the in 1 Referring to the embodiment shown.

List of reference symbols

1

Hybrid electric drive

2

Electric motor

3

Internal combustion engine

4th

Exhaust aftertreatment system

5

arrow

6th

Diesel oxidation catalyst

7th

Particulate filter

8th

SCR catalytic converter

9

Facility

10

Control and / or regulating electronics

11

Exhaust aftertreatment unit

Claims (8)

Method for suppressing ammonia slip during operation of an SCR catalytic converter (8) of a hybrid electric drive (1), in particular a motor vehicle, the temperature of an exhaust gas from the hybrid electric drive (1) flowing through the SCR catalytic converter (8) depending on a predetermined limit temperature of the SCR -Catalyst (8), beyond which an uncontrolled release of ammonia stored in the SCR catalyst (8) occurs, is regulated in such a way that a temperature of the SCR catalyst (8) does not exceed the predetermined limit temperature, a space velocity of the SCR -Catalyst (8) is controlled as a function of the predetermined limit temperature of the SCR catalyst (8) in such a way that the temperature of the SCR catalyst (8) does not exceed the predetermined limit temperature and the space velocity of the SCR catalyst (8) is controlled by Parameters of an exhaust gas recirculation of the hybrid electric drive (1) and / or parameters of a cylinder The filling of cylinders of the internal combustion engine (3) is regulated. Procedure according to Claim 1 , characterized in that the temperature of the exhaust gas is regulated in that, when the predetermined limit temperature is reached, a drive torque generated by the hybrid electric drive (1) is at least partially applied by at least one electric motor (2) of the hybrid electric drive (1). Procedure according to Claim 1 or 2 , characterized in that when the predetermined limit temperature is reached, a maximum drive torque that can be generated by an internal combustion engine (3) of the hybrid electric drive (1) is limited to a predetermined maximum drive torque. Method according to one of the Claims 1 until 3 , characterized in that a space velocity of the SCR catalytic converter (8) is regulated by regulating an engine speed of the internal combustion engine (3). Having a hybrid electric drive (1), in particular for a motor vehicle - At least one electric motor (2) and at least one internal combustion engine (3), with each of which a drive power can be provided, - At least one SCR catalytic converter (8) connected downstream of the internal combustion engine (3), - At least one sensor device (9) for detecting a temperature of the SCR catalytic converter (8), with which temperature signals corresponding to the respective detected temperature of the SCR catalytic converter (8) and associated with the SCR catalytic converter (8) can be generated, and - At least one control and / or regulating electronics (10) which are signal-connected to the electric motor (2), the internal combustion engine (3) and the sensor device (9) and are set up to control the electric motor (2) and the internal combustion engine (3) , - The control and / or regulating electronics (10) being set up to determine from the temperature signals assigned to the SCR catalytic converter (8) whether the temperature of the SCR catalytic converter (8) is a predetermined limit temperature of the SCR catalytic converter (8), beyond which an uncontrolled release of ammonia stored in the SCR catalytic converter (8) takes place and, after the temperature of the SCR catalytic converter (8) has reached the specified limit temperature, - at least temporarily to control the electric motor (2) and the internal combustion engine (3) in such a way that a drive torque generated by the hybrid electric drive (1) can at least partially be applied by the electric motor (2), and - The control and / or regulating electronics are set up for regulating a space velocity of the SCR catalytic converter (8) as a function of the predetermined limit temperature of the SCR catalytic converter (8) so that the temperature of the SCR catalytic converter (8) does not exceed the predetermined limit temperature , and the control and / or regulating electronics (10) is set up, a space velocity of the SCR catalytic converter (8) by regulating parameters of an exhaust gas recirculation of the hybrid electric drive (1) and / or of parameters of a cylinder filling of cylinders of the internal combustion engine (3) to regulate. Hybrid electric drive (1) after Claim 5 , characterized in that the control and / or regulating electronics (10) is set up to limit a maximum drive torque that can be generated by the internal combustion engine (3) to a specified maximum drive torque after the temperature of the SCR catalytic converter (8) has reached the specified limit temperature Has. Hybrid electric drive (1) after Claim 5 or 6th , characterized in that the control and / or regulating electronics (10) are set up to set a space velocity of the SCR catalytic converter (8) by regulating parameters of an exhaust gas recirculation of the hybrid electric drive (1) and / or of parameters of a cylinder filling of cylinders of the internal combustion engine (3) to regulate after the temperature of the SCR catalytic converter (8) has reached the specified limit temperature. Hybrid electric drive (1) after Claim 5 or 6th , characterized in that the control and / or regulating electronics (10) are set up to regulate a space velocity of the SCR catalytic converter (8) by regulating an engine speed of the internal combustion engine (3) after the temperature of the SCR catalytic converter (8) has reached the specified limit temperature.

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